1. Field of the Invention
The present invention relates to an expectorant comprising a hydroxyalkylcysteine derivative as an active ingredient.
2. Description of the Background
Up to the present time, S-(2-hydroxyethyl)-L-cysteine [Journal of Pharmaceutical Sciences, 50. 312 (1961)] and S-(3-hydroxypropyl)-L-cysteine [Biochem. J. 100, 362 (1966)] are known as hydroxyalkylcysteine derivatives. However, all that has been reported concerning their pharmacological effects is that S-(2-hydroxyethyl)-L-cysteine has anti-seborrheic activity (West German Laid-open Patent No. 2,219,726) and that S-(3-hydroxypropyl)-L-cysteine is effective against anti-cholesterolemia and arteriosclerosis (U.S. Pat. No. 3,892,852).
On the other hand, cysteine derivatives such as carbocysteine, N-acetylcysteine, cysteine ethyl ester hydrochloride, and the like are being used as expectorants.
The cysteine derivatives described above when used in expectorants are not completely satisfactory, particularly both N-acetylcysteine and ethyl ester hydrochloride have the problems of strong toxicity and chemical instability.
Therefore, the development of an expectorant possessing stability, little side effects and toxicity, as well as an excellent expectorant effect, has been desired.
In view of such circumstances, the inventors of the present invention synthesized a number of compounds and examined their pharmacological effects. As a result of these investigations, it was found that the hydroxyalkylcysteine derivative shown by the following formula (I) fulfilled the above conditions and possessed an excellent expectorant effect.